I had tumblr support reset my email for me when I forgot it, I sent them my username, my password, and the IP address I registered the account on (my home one) and it was sufficient enough for them to let me know the email. Have you tried asking if it would be possible to provide that kind of info in order to retrieve the email associated with it? Tumblr support is hella slow, they could probably give TNT a run for their money in the "no-shits-given" department.